I was pretty sure this is incorrect for at least Debian 8 / Jessie based on recollection. And now I'm 100% sure it's false -- sighhttps://www.xkcd.com/386/ -- having just installed it in a VM with only "standard system utility" selected (it is selected by default), and verified that less is installed.

It's using debootstrap --variant=minbase, which (from the man page) "...only includes essential packages and apt." It makes sense that docker would want only the bare minimum. And to be fair, but getting into nit-picking territory, minbase is the default for debootstrap, but debootstrap is not the default method of installing Debian: debian-installer is. So docker's Debian image doesn't install less, but they're not doing a default install, as in invoking debian-installer, and keeping the preselected choices as much as possible.